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HomeNRC LibraryDocument CollectionsGeneric CommunicationsInformation Notices1993

# INFORMATION NOTICE 93-85, Revision 1: Problems with X-Relays in DB- and DHP-Type Circuit Breakers Manufactured by Westinghouse

ACCESSION #: 9401130254                                                        
                                                                               
                              UNITED  STATES                                    
                      NUCLEAR REGULATORY COMMISSION                            
                  OFFICE OF NUCLEAR REACTOR REGULATION                         
                       WASHINGTON      ,      D.C.20555-0001                             
                                                                               
                            January 20, 1994                                   
                                                                               
NRC INFORMATION NOTICE 93-85, REVISION 1:    PROBLEMS WITH X-RELAYS IN         
                                             DB- AND DHP-TYPE CIRCUIT          
                                             BREAKERS MANUFACTURED BY          
                                             WESTINGHOUSE                      
Addressees                                                                     
                                                                               
All holders of operating licenses or construction permits  for nuclear          
power reactors.                                                                
                                                                               
Purpose                                                                        
                                                                               
The U.S. Nuclear Regulatory Commission (NRC) is issuing  this information       
notice revision to correct an  error that identified a Westinghouse             
Electric Company (Westinghouse) DHP-type relay as a  DHB-type relay in the      
original notice. This error  occurred in the original information notice        
title, Purpose and the second  paragraph of the Description of                  
Circumstances. As in the  original, the purpose of this information notice      
is to alert addressees to the  possible failure of the 52X-relay (X-relay)      
to reset in DB- and DHP-type  Westinghouse breakers, thus preventing them       
fromreclosing on demand. It is expected that recipients will review the       
information for applicability to  their facilities and consider actions,        
as appropriate, to avoid similar  problems. However, suggestions contained      
in this information notice are  not NRC requirements; therefore, no             
specific action or written  response is required.                               
                                                                               
Description of Circumstances                                                   
                                                                               
On  June 27, 1993  ,  power to a motor control center was lost at the Haddam       
Neck nuclear power plant.Connecticut  Yankee Atomic Power Company, the         
licensee, determined that the  possible root cause for this event was a         
failure of the X-relay  (anti-pump relay) to reset to the de-energized          
position in a Westinghouse DB-25  circuit breaker.                              
                                                                               
Previously, between July 1 and  August 24, 1984  , the licensee reported          
five incidents in which one  DB-25 and four DHP-250 breakers failed to          
close when required. All five of  those failures were attributed to             
malfunctions of the X-relay. The  licensee believed that dirt had caused        
the problem and instituted a  program for cleaning the stationary and           
moving cores of the relay.                                                     
                                                                               
On  June 11, 1991  ,  and on  January 28, 1992  ,  Duke Power Company reported         
that, at the Oconee Nuclear  Station, X-relays failed to reset and              
prevented the DB-25 breakers  from closing in the Keowee hydroelectric          
generator field and field  flashing circuitry. (The Keoweehydrostation         
supplies emergency power                                                       
                                                                               
                                                                               
                                                  IN 93-85, Revision 1         
                                                  January 20, 1994             
                                                  Page 2 of 3                  
                                                                               
to the  Oconee  station.) The licensee modified the anti-pump function with      
an electrical scheme that does  not require the X-relay.                        
                                                                               
Discussion                                                                     
                                                                               
The X-relay is usually denoted by the symbol 52X in the  electrical             
control circuit schematic diagram  for the breaker. On receipt of a signal      
to close the breaker, the  X-relay energizes and one set of its normally        
open contacts closes to enable  momentary energizing of the breaker             
closing coil. After the breaker  closes, the same set of X-relay contacts       
opens to deenergize the closing coil even though the X-relay remains           
energized by the close signal.  If the close signal is still present after      
the breaker trips, the X-relay  serves to inhibit repeated closure              
attempts until the close signal  is removed. Thus, it provides anti-pump        
protection to the breaker by  preventing repeated breaker closure attempts      
when a standing closure signal  exists after a breaker trips.                   
                                                                               
The armature assembly of an X-relay (see Figure 1) fits  inside a brass         
sleeve and is surrounded by the  electromagnetic coil (different from the       
breaker closing coil) of the  relay. When this coil is energized, the           
plunger (moving core) is drawn  up towards the top cap piece (stationary        
core) of the assembly and the  latch arm operates the relay contacts. In        
its uppermost position, an air  gap is maintained between the                   
bullet-shaped top of the plunger  and the cavity in the cap piece, with         
the shoulder of the plunger  mating with the lip on the cap piece. When         
the coil is de-energized, the  moving core is designed to fall, by              
gravity, into its lowest  position. The failure of the moving core to fall      
to its lowest position is the  possible failure mode of interest at Haddam      
Neck.                                                                          
                                                                               
Westinghouse and the licensee believe that residual  magnetism associated       
with continuous energization of the relay or mechanical adherence  between      
the two parts are probable  causes for the plunger failing to fall.             
Westinghouse is testing a design enhancement that uses a  brass spacer          
between the moving and  stationary cores to create a controlled air gap.        
Westinghouse plans to issue a Nuclear Safety Advisory  Letter to notify         
users of this problem. The  licensee is evaluating a design modification        
for the X-relay function in the  motor control center.                          
                                                                               
                                                                               
                                                  IN 93-85, Revision 1         
                                                  January 20, 1994             
                                                  Page 3 of 3                  
                                                                               
This information notice requires no specific action or  written response.       
If you have any questions about the information in this  notice, please         
contact one of the technical  contacts listed below or the appropriate          
office of Nuclear Reactor  Regulation (NRR) project manager.                    
                                                                               
                                                                               
                              Brian K. Grimes,  Director                        
                              Division of  Operating Reactor Support            
                              Office of Nuclear  Reactor Regulation             
                                                                               
Technical contacts: KamalakarNaidu, NRR                                       
                    (301) 504-2980                                             
                                                                               
                    Frederick H. Burrows, NRR                                  
                    (301) 504-2901                                             
                                                                               
Attachments:                                                                   
1.   Figure 1,  X-Relay Magnetic Core                                           
2.   List of  Recently Issued NRC Information Notices                           
                                                                               
                                                                               
                                                  Attachment 1                 
                                                  IN 93-85, Rev. 1             
                                                  January 20, 1994             
                                                  Page 1 of 1                  
                                                                               
Figure 1 "X-relay Magnetic Core" omitted.                                      
                                                                               
                                                                               
                                                  Attachment 2                 
                                                  IN 93-85, Rev. 1             
                                                  January 20, 1994             
                                                  Page 1 of 1                  
                                                                               
                         LIST OF RECENTLY ISSUED                               
                         NRC INFORMATION  NOTICES                               
                                                                               
Information                        Date of                                     
Notice No.    Subject              Issuance  Issued to                         
                                                                               
94-05   Potential  Failure of       01/19/94  All holders of OLs or CPs         
        Steam  Generator Tubes                for pressurized water             
        with Kinetically Welded              reactors (PWRs).                  
        Sleeves                                                                
                                                                               
94-04   Digital  Integrated         01/14/94  All NRC licensees  except          
        Circuit  Sockets with                 licensed  operators.               
        Intermittent Contact                                                   
                                                                               
94-03   Deficiencies Identified    01/11/94  All holders of OLs or CPs         
        during Service Water System          for nuclear power reactors.       
        Operational  Performance                                                
        Inspections                                                            
                                                                               
94-02   Inoperability of General   01/07/94  All holders of OLs or CPs         
        Electric Magne-Blast                 for nuclear power reactors.       
        Breaker  Because of Mis-                                                
        alignment of Close-Latch                                               
        Spring                                                                 
                                                                               
94-01   Turbine  Blade Failures     01/07/94  All holders of OLs or CPs         
        Caused by Torsional                  for nuclear power reactors.       
        Excitation  from Electrical                                             
        System  Disturbance                                                     
                                                                               
93-101  Jet Pump Hold-Down Beam    12/17/93  All holders of OLs or CPs         
        Failure                              for boiling-water reactors.       
                                                                               
93-100  Reporting Requirements     12/22/93  All  U.S.  Nuclear Regulatory       
        for Bankruptcy                       Commission licensees.             
                                                                               
91-29,  Potential Deficiencies     12/22/93  All holders of OLs or CPs         
Supp. 2 Found During Electrical              for nuclear power reactors.       
        Distribution System                                                    
        Functional  Inspections                                                 
                                                                               
93-99   Undervoltage Relay and     12/21/93  All holders of OLs and CPs        
        Thermal  Overload Setpoint            for nuclear power reactors.       
        Problems                                                               
                                                                               
OL = Operating License                                                         
CP = Construction Permit                                                       
                                                                               
                                                                               
*** END OF DOCUMENT ***                                                                               
                                                                               
                                                                               
 
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